I. Field of the Invention
This invention relates to oil well tools having means for providing supplementary lubrication of the bearing assembly thereof and, in particular, to a porous seal element which allows the flow of the drilling media into the bearing assembly while filtering damaging particulates.
II. Description of the Prior Art
Sealed bearing and lubrication assemblies for oil tools, such as cutters and roller reamers, are widely utilized to extend the useful life of such tools. Without continuous lubrication the heat and friction caused by rotation of the tool will damage the bearings causing a breakdown of the tool. Similarly, without seals to enclose the bearing housing, damaging particles will flow into the apparatus while lubricant will escape therefrom. In either event, the useful life of the tool will be severely limited. Thus, such rotating tools are generally provided with a lubrication reservoir and seal elements to extend the life of the tool.
An example of such a sealed bearing system is shown in U.S. Pat. No. 4,182,425 directed to a reamer having a pressure compensated sealed bearing assembly. It was found, however, that the bearing design with an initial supply of lubricant would outlast the tungsten carbide cutting elements and therefore the inclusion of a supplemental supply of lubricant was unnecessary. With the improvement of the cutter elements to extend their useful life, improved sealing and lubrication systems are necessary. The pressure compensated lubrication reservoir, which depends upon down hole pressure to provide a continuous supply of lubricant, can be costly to manufacture and may malfunction or become depleted resulting in damage to the tool.
Other systems have been developed which utilize the lubricating properties of the drilling media. These assemblies permit free flow through the tool in order to allow the drilling media to lubricate the bearing assembly. However, because of the formation cutting particles found in these down hole fluids, damage and malfunction were often the end results of such systems. Thus, such tools had a short useful life requiring frequent replacement.